It has already been proposed in the prior art to provide a number of different arrangements for indicating the direction of rotation, that is to say the sign of the angle of rotation measured, and also, where necessary, to count the number of rotations effected by the steering column. In particular, such arrangements include at least one disc, the rotation of which follows variation in the angle which is required to be measured. The periphery of this disc cooperates with a suitable measuring means for measuring the angle of rotation. In the prior art, a sensor of this kind is commonly called an incremental angular coder. In such a device, the disc includes recesses or tracks, which serve as indicia that pass in front of a given type of reading device. The reading device produces a pulse on a measuring signal which can be processed electronically in such a way as to give the absolute angle of steer, the rate at which the angle of steer is varying, the direction of rotation, and (if required) the number of rotations effected.
Up to the present time in the prior art, such arrangements call for expensive means for counting the number of turns by memorising the pulse count, providing supplementary indicia tracks and so on.